Group III-V semiconductor device with strain-relieving layers

ABSTRACT

According to one exemplary embodiment, a group III-V semiconductor device includes at least one transition layer situated over a substrate. The group III-V semiconductor device further includes a first strain-relieving interlayer situated over the at least one transition layer and a second strain-relieving interlayer situated over the first strain-relieving interlayer. The group III-V semiconductor device further includes a first group III-V semiconductor body situated over the second strain-relieving interlayer. The first and second strain-relieving interlayers comprise different semiconductor materials so as to reduce a strain in the first group III-V semiconductor body. The second strain-relieving interlayer can be substantially thinner than the first strain-relieving interlayer.

This is a continuation of application Ser. No. 14/069,139 filed on Oct.31, 2013, which is itself a continuation of application Ser. No.12/587,964 filed Oct. 14, 2009, now U.S. Pat. No. 8,575,660. Thedisclosures in the above-identified patent applications are herebyincorporated fully by reference into the present application.

BACKGROUND OF THE INVENTION

In the present application, “group III-V semiconductor” refers to acompound semiconductor that includes at least one group III element andat least one group V element, such as, but not limited to, galliumnitride (GaN), gallium arsenide (GaAs), indium aluminum gallium nitride(InAlGaN), indium gallium nitride (InGaN) and the like. Analogously,“III-nitride semiconductor” refers to a compound semiconductor thatincludes nitrogen and at least one group III element, such as, but notlimited to, GaN, AlGaN, InN, AlN, InGaN, InAlGaN and the like.

1. Field of the Invention

The present invention is generally in the field of semiconductors. Moreparticularly, the invention is in the field of fabrication of compoundsemiconductor devices.

2. Background Art

A group III-V semiconductor device, such as a group III-V semiconductorheterojunction field effect transistor (HFET), can utilize a firstsemiconductor body comprising gallium nitride (GaN) and a secondsemiconductor body comprising aluminum gallium nitride (AlGaN) toachieve a high current conduction channel between the two semiconductorbodies. The group III-V semiconductor device can include a buffer layerbetween a silicon substrate and the first semiconductor body, where thebuffer layer can comprise a group III-V semiconductor material such asaluminum nitride (AlN). However, forming the buffer layer on the siliconsubstrate can cause a strain in the first semiconductor body as a resultof a difference in crystal lattice structure and thermal coefficient ofexpansion between the silicon substrate and the buffer layer.

If the first semiconductor body is too thick, the strain in the firstsemiconductor body can cause cracking in the epitaxial layers in thegroup III-V semiconductor device and/or cause an undesirable amount ofwafer warping during device fabrication. However, for high voltageapplications, the first semiconductor body requires a correspondinglyhigh breakdown voltage, which is directly related to the thickness ofthe semiconductor body. For example, high voltage applications canrequire a breakdown voltage greater than approximately 300.0 volts.Thus, it is desirable to reduce the strain in the first semiconductorbody so that its thickness can be sufficiently increased so as toprovide a sufficiently high breakdown voltage for high voltageapplications.

In a conventional approach for reducing the strain in the firstsemiconductor body of a conventional group III-V semiconductor device, afirst transition layer comprising AlGaN can be formed over the bufferlayer and a second transition layer comprising AlGaN with a loweraluminum composition can be formed over the first transition layer. Inthe conventional approach, the first and second transition layers canprovide some strain reduction in the first semiconductor body. However,additional strain relief in the first semiconductor body may benecessary so as to allow its thickness to be sufficiently increased forhigh voltage applications without causing epitaxial layer crackingand/or an undesirable amount of wafer warping.

SUMMARY OF THE INVENTION

Group III-V semiconductor device with strain-relieving interlayers,substantially as shown in and/or described in connection with at leastone of the figures, and as set forth more completely in the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a cross-sectional diagram of an exemplaryconventional group III-V semiconductor device situated over a substrate.

FIG. 2 illustrates a cross-sectional diagram of an exemplary group III-Vsemiconductor device with exemplary strain-relieving interlayerssituated over a substrate in accordance with one embodiment of thepresent invention.

FIG. 3 shows a flowchart illustrating an exemplary method for forming agroup III-V semiconductor device with strain-relieving interlayers inaccordance with one embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is directed to a group III-V semiconductor devicewith strain-relieving interlayers. The following description containsspecific information pertaining to the implementation of the presentinvention. One skilled in the art will recognize that the presentinvention may be implemented in a manner different from thatspecifically discussed in the present application. Moreover, some of thespecific details of the invention are not discussed in order not toobscure the invention.

The drawings in the present application and their accompanying detaileddescription are directed to merely exemplary embodiments of theinvention. To maintain brevity, other embodiments of the presentinvention are not specifically described in the present application andare not specifically illustrated by the present drawings.

FIG. 1 shows a cross-sectional diagram of an exemplary conventionalgroup III-V semiconductor device situated on a substrate. Semiconductorstructure 100 includes conventional group III-V semiconductor device 102(also referred to simply as “conventional semiconductor device 102” inthe patent application), which is situated on substrate 104.Conventional semiconductor device 102, which can be a group III-Vsemiconductor HFET, includes buffer layer 106, transition layers 108 and110, group III-V semiconductor body 112 (also referred to simply as“semiconductor body 112” in the patent application), group III-Vsemiconductor body 114 (also referred to simply as “semiconductor body114” in the patent application), source electrode 116, drain electrode118, and gate electrode 120.

As shown in FIG. 1, buffer layer 106 is situated over substrate 104,which can be a silicon substrate. Buffer layer 106 can comprise aluminumnitride (AlN) and has thickness 122, which can be from approximately 0.2microns to approximately 600.0 microns. Buffer layer 106 can be formedby utilizing a metal-organic chemical vapor deposition (MOCVD) processor a molecular beam epitaxy (MBE) deposition process. Also shown in FIG.1, transition layer 108 is situated over buffer layer 106 and transitionlayer 110 is situated over transition layer 108. Transition layer 108can comprise aluminum gallium nitride (AlGaN) with an aluminumcomposition of from approximately 40.0 percent to approximately 60.0percent and transition layer 110 can comprise AlGaN with an aluminumcomposition of from approximately 15.0 percent to approximately 30.0percent. Transition layers 108 and 110 can be formed, for example, byutilizing a MOCVD process or a MBE deposition process. Thickness 124 oftransition layer 108 can be from approximately 0.10 microns toapproximately 0.30 microns and thickness 126 of transition layer 110 canbe from approximately 0.20 microns to approximately 0.50 microns.

Further shown in FIG. 1, semiconductor body 112 is situated overtransition layer 110 and semiconductor body 114 is situated oversemiconductor body 112. Semiconductor body 112 can comprise galliumnitride (GaN) and semiconductor body 114 can comprise AlGaN, which canhave an aluminum composition from approximately 18.0 percent toapproximately 28.0 percent. The thickness and composition ofsemiconductor bodies 112 and 114 can be selected so as to generatetwo-dimensional electron gas (2DEG) 128 at or in proximity to theheterojunction of the semiconductor bodies. Thickness 130 ofsemiconductor body 112 can be from approximately 0.6 microns toapproximately 2.5 microns and thickness 132 of semiconductor body 114can be from approximately 8.0 nanometers (nm) to approximately 27.0 nm.Further shown in FIG. 1, source electrode 116, drain electrode 118, andgate electrode 120 are situated over group III-V semiconductor body 114(e.g. AlGaN). Source electrode 116, drain electrode 118, and gateelectrode 120 can each comprise a metal or other conductive material andcan be formed in a manner known in the art.

By utilizing high bandgap group III-V semiconductor materials such asGaN and AlGaN in respective semiconductor bodies 112 and 114, a thinconductive layer (i.e. 2DEG 128) capable of high current conduction canbe provided at the heterojunction of the semiconductor bodies. For highvoltage applications, semiconductor body 112 (e.g. a GaN layer) requiresa correspondingly high breakdown voltage, which is directly related toits thickness (i.e. thickness 130 of semiconductor body 112). Thus, byincreasing thickness 130, the breakdown voltage of semiconductor body112 can be correspondingly increased. However, increasing thickness 130can also increase the strain in semiconductor body 112, which can causeundesirable cracking in the epitaxial layers in semiconductor device102, such as, for example, transition layers 108 and 110 and bufferlayer 106. The increased strain in semiconductor body 112 can alsoundesirably increase wafer warping during fabrication of semiconductordevice 102.

During fabrication of semiconductor device 102, buffer layer 106 (e.g.an AlN layer) can be strained as a result of a difference in crystallattice structure and thermal coefficient of expansion between thesilicon substrate (i.e. substrate 104) and the buffer layer. By reducingthe aluminum composition in transition layer 108 and further reducingthe aluminum composition in transition layer 110, transition layers 108and 110 can reduce some of the strain introduced by buffer layer 106 andtransmitter to semiconductor body 112. However, even with transitionlayers 108 and 110, enough strain can be transmitted to semiconductorbody 112 to prevent its thickness from being increased sufficiently soas to provide the necessary high breakdown voltage required for highvoltage operation without causing cracking in the epitaxial layers insemiconductor device 202 and/or causing an unacceptable amount of waferwarping.

FIG. 2 shows a cross-sectional diagram of an exemplary group III-Vsemiconductor device with exemplary strain-relieving interlayerssituated on a substrate in accordance with one embodiment of the presentinvention. Semiconductor structure 200 includes group III-Vsemiconductor device 202 (also referred to simply as “semiconductordevice 202” in the patent application), which is situated on substrate204. Semiconductor device 202 can be a group III-V semiconductor HFET,such as a group III-nitride HFET. Semiconductor device 202 includesbuffer layer 206, transition layers 208 and 210, strain-relievinginterlayers 212 and 214, group III-V semiconductor body 216 (alsoreferred to simply as “semiconductor body 216” in the patentapplication), group III-V semiconductor body 218 (also referred tosimply as “semiconductor body 218” in the patent application), sourceelectrode 220, drain electrode 222, and gate electrode 224.

As shown in FIG. 2, buffer layer 206 is situated over substrate 204,which can be a semiconductor substrate, such as a silicon substrate.Buffer layer 206 can comprise, for example, AlN, and has thickness 226,which can be from approximately 0.2 microns to approximately 600.0microns, for example. Buffer layer 206 can be formed, for example, bydepositing a layer of AlN over substrate 204 by utilizing an MOCVDprocess, an MBE process, or other suitable deposition process. Alsoshown in FIG. 2, transition layer 208 is situated over buffer layer 206and transition layer 210 is situated over transition layer 208.Transition layer 208 can comprise, for example, AlGaN with an aluminumcomposition of from approximately 40.0 percent to approximately 60.0percent, and transition layer 210 can comprise, for example, AlGaN withan aluminum composition of from approximately 15.0 percent toapproximately 30.0 percent.

Transition layer 208 has thickness 228, which can be, for example, fromapproximately 0.10 microns to approximately 0.30 microns. Transitionlayer 210 has thickness 230, which can be, for example, fromapproximately 0.20 microns to approximately 0.50 microns. Transitionlayer 208 can be formed, for example, by depositing a layer of AlGaNover buffer layer 204 by utilizing an MOCVD process, an MBE process, orother deposition process. Transition layer 210 can be formed, forexample, by depositing a layer of AlGaN having a lower aluminumcomposition over transition layer 208 by utilizing an MOCVD process, anMBE process, or other suitable deposition process. In one embodiment ofthe invention, another transition layer comprising AlGaN with a loweraluminum composition than transition layer 210 can be formed overtransition layer 210.

Further shown in FIG. 2, strain-relieving interlayer 212 is situatedover transition layer 210 and strain-relieving interlayer 214 issituated over strain-relieving interlayer 212. Strain-relievinginterlayer 212 can comprise, for example, GaN and has thickness 232.Thickness 232 can be, for example, from approximately 0.20 microns toapproximately 0.5 microns in an embodiment of the invention.Strain-relieving interlayer 212 can be formed, for example, bydepositing a layer of GaN over transition layer 212 by utilizing anMOCVD process, an MBE process, or other suitable deposition process.Strain-relieving interlayer 214 can comprise, for example, AlN and hasthickness 234. In an embodiment of the invention, thickness 234 can be,for example, from approximately 0.01 microns to approximately 0.40microns. Thus, strain-relieving interlayer 212 can be substantiallythicker than strain-relieving interlayer 214 in an embodiment of theinvention. In the present invention, strain-relieving interlayer 212comprises a different semiconductor material than strain-relievinginterlayer 214. In one embodiment, more than two strain-relievinginterlayers can be disposed between transition layer 210 andsemiconductor body 216.

Also shown in FIG. 2, semiconductor body 216 is situated overstrain-relieving interlayer 214 and semiconductor body 218 is situatedover semiconductor body 216. Semiconductor body 216 can comprise a III-Vsemiconductor material such as GaN and has thickness 236. In anembodiment of the invention, thickness 236 of semiconductor body 216 canbe from approximately 0.6 microns to approximately 5.0 microns.Semiconductor body 218 can comprise a III-V semiconductor material, suchas, for example, AlGaN, which can have an aluminum composition of fromapproximately 18.0 percent to approximately 28.0 percent. Semiconductorbody 218 has thickness 238, which can be from approximately 8.0 nm toapproximately 27.0 nm in an embodiment of the invention. Semiconductorbody 218 can have a wider bandgap than semiconductor body 216 as aresult of the difference in composition between semiconductor bodies 216and 218. The thickness and composition of semiconductor bodies 216 and218 can be selected to generate 2DEG (two-dimensional electron gas) 240at or in proximity to the heterojunction of semiconductor bodies 216 and218.

Further shown in FIG. 2, source electrode 220, drain electrode 222, andgate electrode 224 are situated over semiconductor body 218 (e.g. anAlGaN layer). Source electrode 220, drain electrode 222, and gateelectrode 224 can each comprise a metal or other conductive material.Source electrode 220, drain electrode 222, and gate electrode 224 can beformed, for example, by depositing a layer of metal over semiconductorbody 218 by utilizing an evaporation process or other suitable metaldeposition process and appropriately patterning the layer of metal. Inone embodiment of the invention, a dielectric layer can be formedbetween gate electrode 224 and semiconductor body 218.

By utilizing high bandgap group III-V semiconductor materials such asGaN and AlGaN in respective semiconductor bodies 216 and 218, a thinconductive layer (i.e. 2DEG 240) capable of high current conduction canbe formed at the heterojunction (i.e. the interface) of semiconductorbodies 216 and 218.

During fabrication of semiconductor device 202, buffer layer 206 (e.g.an AlN layer) can be strained as a result of a difference in crystallattice structure and thermal coefficient of expansion between substrate204 (e.g. a silicon substrate) and buffer layer 206. Transition layers208 and 210 can be utilized to reduce some of the strain insemiconductor body 216. For example, transition layers 208 and 210 caneach comprise AlGaN, where transition layer 210 has a lower aluminumcomposition than transition layer 212. By reducing the aluminumcomposition of transition layer 210 compared to the aluminum compositionof transistor layer 208, the difference in crystal lattice structurebetween transition layer 210 and semiconductor body 216 can be reducedso as to reduce some of the strain in the semiconductor body.

In an embodiment of the present invention, strain-relieving interlayers212 and 214 are provided between transition layer 210 and semiconductorbody 216 to cause a significant reduction of the strain in semiconductorbody 216. To achieve the strain reduction in semiconductor body 216,strain-relieving interlayers 212 and 214 can comprise respective groupIII-V semiconductor materials that are selected to so as to provide alarge difference in crystal lattice structure between thestrain-relieving interlayers. Strain-relieving interlayers 212 and 214can comprise, for example, GaN and AlN, respectively. In an embodimentof the invention, the strain-relieving interlayers (e.g.strain-relieving interlayers 212 and 214) comprise different group III-Vsemiconductor materials.

Also, strain-relieving interlayer 214 can be substantially thinner thanstrain-relieving interlayer 212. By forming strain-relieving interlayer214 so as to be substantially thinner than strain-relieving interlayer212, the strain in strain-relieving interlayer 214 can be significantlyincreased, thereby further increasing the difference in crystal latticestructure between the strain-relieving interlayers. Thus, by formingstrain-relieving interlayers 212 and 214 from different group III-Vsemiconductor materials and forming strain-relieving interlayer 214 tobe substantially thinner than strain-relieving interlayer 212, anembodiment of the invention can significantly reduce the strain insemiconductor body 216 (e.g. a GaN body).

For high voltage applications, semiconductor body 216 requires acorrespondingly high breakdown voltage, which is directly related to thethickness of the semiconductor body. In an embodiment of the invention,by utilizing strain-relieving interlayers 212 and 214 to significantlyreduce the strain in semiconductor body 216, semiconductor body 216 canhave a sufficient thickness so as to provide a sufficiently highbreakdown voltage as required for high voltage applications. In anembodiment of the invention's semiconductor device, semiconductor body216, which can comprise GaN, can have a sufficient thickness so as toadvantageously provide a breakdown voltage greater than approximately500.0 volts, for example. Thus, an embodiment of the invention canprovide a group III-V semiconductor device that can operate at highvoltage by utilizing strain-relieving interlayers to sufficiently reducethe strain in a group III-V semiconductor body overlying thestrain-relieving interlayers.

FIG. 3 shows a flowchart illustrating an exemplary method forfabricating a III-V semiconductor device with strain-relievinginterlayers according to one embodiment of the present invention.Certain details and features have been left out of flowchart 300 thatare apparent to a person of ordinary skill in the art. For example, astep may consist of one or more substeps or may involve specializedequipment or materials, as known in the art. It is noted that theprocessing steps shown in flowchart 300 are performed on a portion of awafer, which, prior to step 302 of flowchart 300, includes asemiconductor substrate, such as a silicon substrate. The wafer is alsoreferred to as a semiconductor die or simply a die in the presentapplication.

At step 302 of flowchart 300, buffer layer 206 is formed over substrate204, which can be a silicon substrate. Buffer layer 206 can comprise,for example, AlN and can be formed by utilizing an MOCVD process, an MBEprocess, or other suitable deposition process. At step 304 of flowchart300, transition layer 208 is formed over buffer layer 206 and transitionlayer 210 is formed over transition layer 208. For example, transitionlayer 208 can comprise AlGaN with a 40.0 percent to 60.0 percentaluminum composition and transistor layer 210 can comprise AlGaN with a15.0 percent to 30.0 percent aluminum composition. For example,transition layer 210 can have a greater thickness than transition layer208. Transition layers 208 and 210 can be formed, for example, byutilizing an MOCVD process or an MBE process.

At step 306 of flowchart 300, strain-relieving interlayer 212 is formedover transition layer 210 and strain-relieving interlayer 214 is formedover strain-relieving interlayer 212. Strain-relieving interlayers 212and 214 can comprise, for example, GaN and AlN, respectively. Forexample, strain-relieving interlayer 214 can be substantially thinnerthan strain-relieving interlayer 212. For example, strain-relievinginterlayer 214 can have a thickness of from approximately 0.01 micronsto approximately 0.04 microns and strain-relieving interlayer 212 canhave a thickness of from approximately 0.2 microns to approximately 0.5microns. Strain-relieving interlayers 212 and 214 can each be formed,for example, by utilizing an MOCVD process, an MBE process, or othersuitable deposition process.

At step 308 of flowchart 300, semiconductor body 216 is formed overstrain-relieving interlayer 214. Semiconductor body 216 can comprise,for example, GaN and can have a thickness of from approximately 0.6microns to approximately 5.0 microns in an embodiment of the invention.Semiconductor body 216 can be formed, for example, by utilizing an MOCVDprocess, an MBE process, or other suitable deposition process. At step310 of flowchart 300, semiconductor body 218 is formed oversemiconductor body 216 and source electrode 220, drain electrode 222,and gate electrode 224 are formed over semiconductor body 218.Semiconductor body 218 can comprise, for example, AlGaN. The thicknessand composition of semiconductor bodies 216 and 218 can be selected togenerate 2DEG 240 at or in proximity to the heterojunction ofsemiconductor bodies 216 and 218. Semiconductor body 218 can be formed,for example, by utilizing an MOCVD process, an MBE process, or othersuitable deposition process. Source electrode 220, drain electrode 222,and gate electrode 224 can comprise a metal or other conductive materialand can be formed, for example, by depositing a layer of metal oversemiconductor body 218 by utilizing an evaporation process or othersuitable metal deposition process and appropriately patterning the layerof metal.

Thus, as discussed above, an embodiment of the invention provides agroup III-V semiconductor device, such as a group III-V semiconductorHFET, that includes strain-relieving interlayers disposed between atransition layer and a semiconductor body, such as a GaN body, where thestrain-relieving interlayers significantly reduce strain in thesemiconductor body. As a result of the reduced strain in thesemiconductor body, its thickness can be advantageously increased so asto provide a sufficiently high breakdown voltage as required for highvoltage applications without causing epitaxial layer cracking and/orunacceptable wafer warping during device fabrication. Thus, by utilizingstrain-relieving interlayers, an embodiment of the invention can providea semiconductor body, such as GaN body, having a significantly higherbreakdown voltage compared to a semiconductor body, such as a GaN body,in conventional III-V semiconductor device, such as conventional III-Vsemiconductor device 102 in FIG. 1.

From the above description of the invention it is manifest that varioustechniques can be used for implementing the concepts of the presentinvention without departing from its scope. Moreover, while theinvention has been described with specific reference to certainembodiments, a person of ordinary skill in the art would appreciate thatchanges can be made in form and detail without departing from the spiritand the scope of the invention. Thus, the described embodiments are tobe considered in all respects as illustrative and not restrictive. Itshould also be understood that the invention is not limited to theparticular embodiments described herein but is capable of manyrearrangements, modifications, and substitutions without departing fromthe scope of the invention.

The invention claimed is:
 1. A group III-V semiconductor devicecomprising: at least one buffer layer situated over a substrate; atleast one transition layer situated over said at least one buffer layer,said at least one transition layer and said at least one buffer layercomprising different semiconductor materials; a first strain-relievinginterlayer situated over said at least one transition layer and a secondstrain-relieving interlayer situated over said first strain-relievinginterlayer; and a first group III-V semiconductor body situated oversaid second strain-relieving interlayer, wherein said first and secondstrain-relieving interlayers comprise different semiconductor materialsso as to reduce a strain in said first group III-V semiconductor body,wherein said first strain-relieving interlayer has a thickness greaterthan or substantially equal to 0.2 micrometers, wherein said secondstrain-relieving interlayer has a thickness greater than orsubstantially equal to 0.01 micrometers, wherein said firststrain-relieving interlayer is thicker than said second strain-relievinginterlayer.
 2. The group III-V semiconductor device of claim 1, whereinsaid first strain-relieving interlayer comprises gallium nitride (GaN).3. The group III-V semiconductor device of claim 1, wherein said secondstrain-relieving interlayer comprises aluminum nitride (AlN).
 4. Thegroup III-V semiconductor device of claim 1, wherein said at least onetransition layer comprises a first transition layer of aluminum galliumnitride (AlGaN) and a second transition layer of aluminum galliumnitride (AlGaN), wherein said second transition layer has a loweraluminum composition than said first transition layer.
 5. The groupIII-V semiconductor device of claim 1, further comprising a second groupIII-V semiconductor body situated over said first group III-Vsemiconductor body, wherein a two-dimensional electron gas (2DEG) formsat a heterojunction of said first and second group III-V semiconductorbodies.
 6. The group III-V semiconductor device of claim 1, wherein saidfirst group III-V semiconductor body provides a breakdown voltagegreater than approximately 500 volts.
 7. The group III-V semiconductordevice of claim 1, wherein said first group III-V semiconductor body hasa thickness in a range between 2.5 microns and 5.0 microns.
 8. A groupIII-V semiconductor device comprising: at least one buffer layersituated over a substrate; at least one transition layer situated oversaid at least one buffer layer, said at least one transition layer andsaid at least one buffer layer comprising different semiconductormaterials; a first strain-relieving interlayer situated over said atleast one transition layer and a second strain-relieving interlayersituated over said first strain-relieving interlayer; and a first groupIII-V semiconductor body situated over said second strain-relievinginterlayer, wherein said first and second strain-relieving interlayerscomprise different semiconductor materials so as to reduce a strain insaid first group III-V semiconductor body, wherein said firststrain-relieving interlayer has a thickness greater than orsubstantially equal to 0.2 micrometers, wherein said secondstrain-relieving interlayer has a thickness greater than orsubstantially equal to 0.01 micrometers, wherein said first group III-Vsemiconductor body has a thickness greater 2.5 microns, wherein saidfirst strain-relieving interlayer is thicker than said secondstrain-relieving interlayer, wherein said second strain-relievinginterlayer comprises an aluminum nitride (AlN) layer.
 9. The group III-Vsemiconductor device of claim 8, further comprising a buffer layerdisposed between said substrate and said at least one transition layer.10. The group III-V semiconductor device of claim 8, wherein said firststrain-relieving interlayer comprises gallium nitride (GaN).
 11. Thegroup III-V semiconductor device of claim 8, wherein said at least onetransition layer comprises a first transition layer of aluminum galliumnitride (AlGaN) and a second transition layer of aluminum galliumnitride (AlGaN), wherein said second transition layer has a loweraluminum composition than said first transition layer.
 12. The groupIII-V semiconductor device of claim 8, further comprising a second groupIII-V semiconductor body situated over said first group III-Vsemiconductor body, wherein a two-dimensional electron gas (2DEG) formsat a heterojunction of said first and second group III-V semiconductorbodies.
 13. The group III-V semiconductor device of claim 8, whereinsaid first group III-V semiconductor body provides a breakdown voltagegreater than approximately 500 volts.
 14. The group III-V semiconductordevice of claim 8, wherein said first group III-V semiconductor body hasa thickness in a range between 2.5 microns and 5.0 microns.
 15. A methodfor forming a group III-V semiconductor device over a substrate, saidmethod comprising: forming at least one buffer layer situated over saidsubstrate; forming at least one transition layer situated over said atleast one buffer layer, said at least one transition layer and said atleast one buffer layer comprising different semiconductor materials;forming a first strain-relieving interlayer of a thickness greater thanor substantially equal to 0.2 micrometers over said at least onetransition layer and a second strain-relieving interlayer of a thicknessgreater than or substantially equal to 0.01 micrometers over said firststrain-relieving interlayer, said first and second strain-relievinginterlayers comprising different group III-V semiconductor materials,said first strain-relieving interlayer being thicker than said secondstrain-relieving interlayer; and forming a first group III-Vsemiconductor body over said second strain-relieving interlayer.
 16. Themethod of claim 15, wherein said first strain-relieving interlayercomprises gallium nitride (GaN).
 17. The method of claim 15, whereinsaid second strain-relieving interlayer comprises aluminum nitride(AlN).
 18. The method of claim 15, wherein said at least one transitionlayer comprises a first transition layer of aluminum gallium nitride(AlGaN) and a second transition layer of aluminum gallium nitride(AlGaN), wherein said second transition layer has a lower aluminumcomposition than said first transition layer.
 19. The method of claim15, further comprising forming a second group III-V semiconductor bodyover said first group III-V semiconductor body, wherein atwo-dimensional electron gas (2DEG) is formed at a heterojunction ofsaid first and second group III-V semiconductor bodies.
 20. The methodof claim 15, wherein said first group III-V semiconductor body providesa breakdown voltage greater than approximately 500 volts.